xxiv. Proceedings. \_May 2nd, 1922. 



Ordinary Meeting, April 25th, 1922. 

 A vote of thanks was passed to the donors of the books upon 

 the table. 



Mr. W. J. Perry, B.A., read a paper entitled : — 



"On the Cultural Significance of the Use of Stone." 



This paper is printed in the Memoirs. 



vSpecial Meeting, May and, 1922. 



Mr. T. A. Coward, M.Sc., F.Z.S., F.E.S. (President), in the 



Chair. 



Sir William Boyd Dawkins, M.A., D.Sc., F.R.S., read a paper 

 entitled :- u -p^e Crust of the Earth." 



In view of the recent discussion in the Society and in the 

 Press relating to the crust of the earth, it is desirable to define 

 the current theory held by the leading geologists for the last 

 sixty years. The theory is founded on the researches of eminent 

 mathematicians, chemists and physicists such as Helmholtz, 

 Kelvin, Hopkins, Bishoff, and Durocher, and has been accepted 

 by zoologists and botanists — Huxley, Darwin, Wallace, Sclater, 

 as an adequate explanation of the distribution of plants and 

 animals, not only on the present surface of the earth, but also 

 in the remote past revealed in the geological record. 



The crust of the earth is that portion of the solid rock that is 

 open to observation. It is of unknown and probably varying 

 thickness, and very thin as compared with the 3962.5 miles of 

 the earth's radius. It is continuous under both sea and land. 



It is composed of rocks arranged in the following downward 

 order : — 



(1) Igneous crj^stallene ; or which have formerly been molten 

 rock. 



(2) Metamorphic ; or rocks altered by heat and pressure. 



(3) Fragmental ; mostly accumulated under the sea. 



The last consists of two well defined groups, the Acid Siliceous 

 such as the granite, and the Basic or Basaltic, such a3 the 

 Gabbros, difiering in their chemistry, and being related to one 

 another as oil is to water. It is therefore probable that the first 

 crust formed on the cooling earth belonged to the siliceous 

 group, and that the basic solidified at a later time. Durocher 

 points out that both these groups are derived from two distinct 

 inagmas or zones of highly heated matter, which if cooled slowly 

 under high pressure and in presence of water, take the largely 

 crystalline structure of granite and gabbro, and other Plutonic 

 tocks, while if, as in the volcanic rock that cool swiftly under 

 less pressure, they are micro-crystalline or vitreous. 



